which is the classical Carnot limit for the efficiency. It is worth noticing that the processes preventing the engine from reaching efficiencies arbitrarily close to the bound in Eq. (REF ) (the ones represented by \(\Delta \mathcal {Q}^{NR}\) ), are the same ones enforcing the third law of thermodynamics in the form of Nernst's unattainability principle [1]}, [2]}.
